1. Field of the Invention
The present invention relates to an exposure apparatus for manufacturing a semiconductor integrated circuit and a device manufacturing method which can use the exposure device and, more particularly, to improvement of driving of a substrate stage on which a substrate such as a wafer two-dimensionally moves in an exposure reference plane.
2. Description of the Related Art
In the lithography process in manufacturing a semiconductor integrated circuit, a reduction-projection type exposure device using a step-and-repeat scheme, i.e., a so-called stepper is popularly used. FIG. 7 shows the arrangement of the stepper. Referring to FIG. 7, reference numeral 71 denotes a wafer; 72, an X stage constituting a wafer stage; 73, a Y stage constituting a wafer stage; 74, an X-stage drive linear motor; 75, a Y-stage drive linear motor; 76, a measurement mirror, 77, an X-stage position measurement laser beam; 78, a Y-stage position measurement laser beam; 79, an X-stage position measurement laser interferometer; 80, a Y-stage position measurement laser interferometer; 81, a reduction-projection lens; and 82, a reticle. This device also comprises a light source for ultraviolet rays, X-rays, or the like (not shown).
In such a semiconductor reduction exposure device, a micropattern drawn on the reticle 82 is reduced to 1/5 by the reduction-projection lens 81 by means of a light source for ultraviolet rays, X-rays, or the like to expose and transfer the reduced pattern onto the wafer 71. At this time, the wafer 71 is sequentially exposed while an X-Y drive called step-and-repeat is repeated by the X and Y wafer stages 72 and 73. This X-Y drive depends on a position measured by the laser interferometers 79 and 80 to drive linear motors 74 and 75, thereby positioning the wafer stages 72 and 73.
FIG. 4 shows a conventional drive method for a wafer stage in the X-Y drive. The abscissa indicates time, and the ordinate indicates a velocity. Reference symbols S1 to S4 denote lines representing the difference between velocity patterns caused by the difference between stage moving amounts. The line S1 having a small stage moving amount represents a velocity pattern in which, after the stage is maximally accelerated, the maximum deceleration is performed, such that the velocity does not reach the highest velocity V1, to move the stage to a target position. In contrast to this, the line S4 having a larger stage moving amount represents a pattern in which a stage is maximally accelerated to the highest velocity V1, constant-velocity movement at the highest velocity V1 is performed, and maximum deceleration is performed to move the stage to a target position.
As basic performances required in the stepper shown in FIG. 7, superposition precision and throughput are known. The wafer stage is an important mechanism which affects the performances. The positioning precision of the wafer stage considerably influences the superposition precision, and the drive time of the wafer stage considerably influences the throughput.
The drive time and positioning precision of the wafer stage are conflicting elements, and it is considerably difficult to improve both performances, i.e., both the drive time and the positioning precision. More specifically, increases in maximum acceleration and highest velocity of the velocity pattern of the wafer stage largely contribute to shortening of drive time. However, when the maximum acceleration and the highest velocity are increased, the amplitude of vibration of the stepper body serving as a base for supporting the wafer stage increases. The vibration serves as a disturbance to degrade the positioning precision of the wafer stage. For example, as shown in FIG. 5A, the drive time of a velocity pattern p2 is shorter than the drive time of a velocity pattern p1 such that the highest velocity of the velocity pattern p2 is increased. However, as shown in corresponding FIG. 5B, the amplitude of vibration of the body increases because a body displacement h2 in the velocity pattern p2 is larger than a body displacement h1 in the velocity pattern p1. In particular, residual vibration upon completion of the drive operates as a disturbance in positioning to cause degradation of the positioning precision.
For this reason, the maximum acceleration and the highest velocity of the velocity pattern of the wafer stage in a conventional stepper are set to satisfy the highest superposition precision required in the stepper, and these acceleration and velocity are fixed.